ALBERT

Description: In this paper, we outline the need for a coordinated international effort toward the building of an open-access Global Ocean Oxygen Database and ATlas (GO2DAT) complying with the FAIR principles (Findable, Accessible, Interoperable, and Reusable). GO2DAT will combine data from the coastal and open ocean, as measured by the chemical Winkler titration method or by sensors (e.g., optodes, electrodes) from Eulerian and Lagrangian platforms (e.g., ships, moorings, profiling floats, gliders, ships of opportunities, marine mammals, cabled observatories). GO2DAT will further adopt a community-agreed, fully documented metadata format and a consistent quality control (QC) procedure and quality flagging (QF) system. GO2DAT will serve to support the development of advanced data analysis and biogeochemical models for improving our mapping, understanding and forecasting capabilities for ocean O2 changes and deoxygenation trends. It will offer the opportunity to develop quality-controlled data synthesis products with unprecedented spatial (vertical and horizontal) and temporal (sub-seasonal to multi-decadal) resolution. These products will support model assessment, improvement and evaluation as well as the development of climate and ocean health indicators. They will further support the decision-making processes associated with the emerging blue economy, the conservation of marine resources and their associated ecosystem services and the development of management tools required by a diverse community of users (e.g., environmental agencies, aquaculture, and fishing sectors). A better knowledge base of the spatial and temporal variations of marine O2 will improve our understanding of the ocean O2 budget, and allow better quantification of the Earth’s carbon and heat budgets. With the ever-increasing need to protect and sustainably manage ocean services, GO2DAT will allow scientists to fully harness the increasing volumes of O2 data already delivered by the expanding global ocean observing system and enable smooth incorporation of much higher quantities of data from autonomous platforms in the open ocean and coastal areas into comprehensive data products in the years to come. This paper aims at engaging the community (e.g., scientists, data managers, policy makers, service users) toward the development of GO2DAT within the framework of the UN Global Ocean Oxygen Decade (GOOD) program recently endorsed by IOC-UNESCO. A roadmap toward GO2DAT is proposed highlighting the efforts needed (e.g., in terms of human resources).

Description: From 2008 through 2019, a comprehensive research project, SFB 754, Climate - Biogeochemistry Interactions in the Tropical Ocean, was funded by the German Research Foundation to investigate the climate-biogeochemistry interactions in the tropical ocean with a particular emphasis on the processes determining the oxygen distribution. During three 4-year long funding phases, a consortium of more than 150 scientists conducted or participated in 34 major research cruises and collected a wealth of physical, biological, chemical, and meteorological data. A common data policy agreed upon at the initiation of the project provided the basis for the open publication of all data. Here we provide an inventory of this unique data set and briefly summarize the various data acquisition and processing methods used.

Description: In the Peruvian upwelling area, benthic biogeochemical fieldwork focused on the FS Meteor cruises M77/1, M77/2, M92, M136, and M137. Off Mauritania, benthic investigations were mainly conducted on FS Maria S. Merian cruise MSM17/4 and FS Meteor cruise M107 (Sommer et al., 2021; see Table 2 and supplementary Tables S29 to S35). Research questions addressed organic carbon degradation, associated element cycling, and solute fluxes in the benthic boundary layer in response to variable bottom water redox conditions and hydrodynamic forcing (e.g. Bohlen et al., 2011; Dale et al., 2014; Dale et al., 2016; Dale et al., 2019; Dale et al., 2021; Loginova et al., 2020; Lomnitz et al., 2016; Noffke et al., 2012; Plass et al., 2020; Schroller-Lomnitz et al., 2019; Sommer et al., 2016). Effects of variable bottom water conditions on seabed nutrient and trace metal release were studied during in situ and ex situ on-board sediment incubations and the analysis of pore water geochemistry. Further emphasis was placed on resolving the imprint of specific microbial processes and foraminiferal metabolic activity on element turnover and exchange across the sediment water interface (e.g. Glock et al., 2013, 2019, 2020; Gier et al., 2016, 2017; Scholz et al., 2016; 2017). The results were further interpreted using benthic numerical models (e.g. Bohlen et al., 2011; Dale et al., 2014, 2015, 2016, 2017, 2019).

Description: Dinitrogen (N2) and carbon (C) fixation rates were measured on 9 cruises (see Table C17) using shipboard incubation experiments, complemented with nutrient and oxygen manipulations. During cruises M77/3, M77/4 and M80/2, N2 fixation was measured using the bubble addition method following Montoya et al (1996). During M80/2 a novel method based on 360 15N2 gas pre-dissolution, which was developed by Mohr et al. (2010), was tested in parallel to the classic method. An underestimation of N2 fixation rates by the classic method has been observed (Großkopf et al., 2012) and therefore the novel 'pre-dissolution method' was applied during the following cruises (M83/1, M90, M91, M93, M97, M104, M107). Single cell N2 fixation rates to differentiate the contribution of different clades of N2 fixers were measured using a NanoSIMS (Martinez-Perez et al., 2016).

Description: Potential rates for microaerobic respiration and aerobic organic matter degradation as a source of ammonia (NH4+) in the Peruvian OMZ was assessed using an 18O2 labelling approach suitable for microaerobic respiration (Holtappels et al., 2014). Further, the effects of O2 depletion associated with marine snow particles on microbial respiration was explored by combining 18O2 labelling experiments with in-situ particle size analysis and modelling of aggregate-size dependent respiration (Kalvelage et al., 2015). Anammox, denitrification, and nitrification, as well as N2O production rates were measured on several cruises (Kalvelage et al., 2011; Löscher et al., 2012; Callbeck et al., 2017; Bourbonnais et al., 2017; Frey et al., 2020) using isotope fractionation studies, 15N tracer additions, and inhibitor studies.

Description: LADCP measurements were performed on all research cruises that concentrated on open ocean areas (see Table C3) while on cruises that worked mostly in shallow waters, ocean current measurements by the shipboard ADCP (see section 4.1.8) were deemed sufficient. GEOMAR used a two-instrument configuration with two Teledyne RDI 300 kHz workhorse ADCPs mounted in down- and up-looking positions. Data collection and processing was performed according to recommendations in the GO-SHIP manual (Thurnherr et al., 2010).

Description: Ocean turbulence measurement programs were carried out during 22 cruises to quantify the dissipation rate of turbulent kinetic energy and infer rates of turbulent mixing (see Table C6). The used shipboard microstructure profiling systems 165 (MSS) were manufactured by Sea & Sun Technology and consisted of a profiler (MSS90-D, S/N 26, 32 and 73), a winch having 500-1000 m of cable and a data interface. All profilers were equipped with three microstructure shear sensors, a fast- response temperature sensor (PF07), an acceleration sensor and two tilt sensors as well as conductivity (Sea & Sun Tech.), temperature (Sea & Sun Tech.), pressure (Keller), turbidity (Seapoint) and oxygen sensors sampling with a lower response time. The profilers were optimized to sink at a rate of 0.5-0.6 m s-1. Standard processing procedures were used to determine 170 the rate of kinetic energy dissipation of turbulence in the water column (see Schafstall et al. (2010) for a detailed description). Additionally, during several autonomous glider missions, a microstructure probe was mounted to the top of the gliders. These probes (MicroRider) were manufactured by Rockland Scientific and carried two microstructure shear and temperature sensors as well as pressure, accelerometer and tilt sensors. The data processing is detailed in Foltz et al. (2020).

Description: CTDO measurements were acquired on the major research cruises performed as part of the SFB 754 or other projects . Seabird 911plus systems equipped with dual temperature-conductivity-oxygen sensors were employed. All systems had a 24-bottle water sampling rosette with 10 l Niskin bottles. On some cruises only 22 bottles were mounted to accommodate a lowered Acoustic Doppler Current Profiler for deep ocean current observations. Water sampling, processing, and calibration followed GO-SHIP recommendations (Swift, 2010; McTaggart et al., 2010; Uchida et al., 2010) and included the recommended steps Data Conversion, Sensor Time-Alignment, Creation of Bottle Files, Outlier Removal, Pressure Sensor Filtering, Conductivity Cell Thermal Mass Correction, Ship Roll Correction and Deck Offset Correction by Loop Editing, as well as Derivation of Calculated Properties. After these steps, conductivity and oxygen readings were calibrated against values determined with salinometry and Winkler titration , respectively. Finally, the downcast data was averaged over 1 dbar wide intervals. An independent upcast calibration was used to obtain calibrated CTDO values coincident with the discrete water samples.

Description: During the second funding phase (2012-2015) a new CTD system became available that could be deployed from a moving 185 ship. First a Teledyne Oceanscience UCTD and later a Teledyne Oceanscience Rapidcast system were acquired and deployed successfully on several cruises (see Table C8). They allowed for the sampling of water masses at high horizontal resolution (ranging from less than 1 km for the Rapidcast system to 10 km for deep UCTD casts) with good accuracy of the pressure, temperature, and conductivity sensors. Processing of the data involved mostly the fall-rate dependent correction of the thermal lag of the conductivity sensor and followed the approach described by Ullman and David (2014). Subsequently 190 the corrected data was calibrated against the calibrated coincident Thermosalinograph and the calibrated nearby CTD data. The typical accuracies of the final pressure, temperature, and salinity data are 1 dbar, 0.01 °C, and 0.01 g/kg, respectively.

Description: The SFB 754 also made a contribution to the global ARGO float program. In 2009, 2911, and 2014 several floats equipped with additional Aanderaa oxygen sensors were deployed off Peru to study the effects of mesoscale eddies on the flow field 200 and the water masses (see Table C10; Czeschel et al., 2018). A number of floats was deployed in the tropical Atlantic to accompany a tracer release experiment (see section 4.2.3). Additionally several of the cruises were used to deploy regular ARGO floats on behalf of the German Hydrographic Office.